Internal combustion engine spark plug assembly



D. WOOLLATT ETAL Filed Sept, 20, 1965 Nov. 17, 1964 United States Patent 3,157,164 INTERNAL COMBUSTION ENGlNE SPARK PLUG ASSEMBLY Derek Woollatt, Buffalo, and Richard W. Szulewski, West Seneca, N.Y., assignors to Worthington Corporation,

Harrison, NJ., a corporation of Delaware Filed Sept. 20, 1963, Ser. No. 310,252 6 Claims. (Cl. 12S-41.32)

This invention relates to spark plug assemblies, and, more particularly, to spark plug assemblies for water jacketed internal combustion engines.

ln these engines, the cylinder head is water jacketed, and the spark plugs for each cylinder are recessed in plug tubes which are bores extending through the jacket forming the cylinder head. The lower or inward closed end of the plug tube forms a part of the top wall of the combustion chamber. This chamber represents the locus of a great amount of heat energy, most of which must be dissipated into the cooling water if overheating of the engine is to be prevented.

The spark plug assembly forming part of the wall of the combustion chamber in this type of engine has presented a substantial problem of heat transfer. The plugs have tended -to overheat, causing a premature breakdown of the plug structure.

In the standard spark plug, a sleeve is threaded at its inner end, and this screws into a similarly threaded opening leading into the combustion chamber. Spaced axially from the inner end of the sleeve is a shoulder which is formed in a plane normal to the longitudinal axis of the plug. A copper washer is positioned between the shoulder and the end wall of the plug tube. The result is that in the assembled structure, there is a substantial air space between the peripheral edge of the copper washer and the wall of the bore or plug tube. The only heat energy transfer, therefore, is along the threaded inner end of the plug sleeve, into the lower wall of the head jacket, and eventually outwardly into the cooling chamber. The eiliciency is of a very low order because of the long heat flux path between the plug and the cooling Water, and because of the relatively small cross-sectional area of the path. In effect, a heat dam is formed.

It is an object of the present invention, therefore, to provide a spark plug assembly which will eliminate the heat dam, providing a greater cross-sectional area for the heat flux to travel from the plug to the cooling water in the head jacket and also providing a shorter travel path for the heat ux.

A further object of the invention is to provide a spark plug assembly which combines the improved heat transfer characteristics with a more eflicient seal between the spark plug and the cylinder head.

With the above and other objects in view, as will be presently apparent, the invention consists in general of certain novel details of construction and combinations of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly claimed.

In the drawings, like characters of reference indicate like parts in the several views, and

FIGURE 1 is a longitudinal section taken through the spark plug assembly of the present invention and illustrating a fragmentary portion of the jacketed cylinder head, including a plug tube in which the spark plug assembly is mounted; and

FiGURE 2 is a cross-sectional view taken on the line 2--2 of FIGURE 1.

1n the drawings, the reference numeral 10 represents a spark plug which is essentially of conventional design except for one portion thereof, which will shortly be more specifically described. A center electrode 11 is mounted in a ceramic insulating sleeve 12. This insulating sleeve is in turn mounted by suitable cement in a metallic outer sleeve 13. This outer sleeve has the usual wrench flats 14, a threaded inner end 15, and the ground electrode 16. Up to this point, the plug structure is conventional. The details thereof may vary widely, and a variety of structures may be used providing the plug presents an outer sleeve.

In carrying out the invention, the outer sleeve 13, between the inner end 15 and the wrench flats 14, is provided with a frusto-conical surface 17, which forms a taper inwardly toward the inner threaded end 15. Outside of and in mating engagement with said frusto-conical gasket 18. This preferably is of copper, but may be of any suitable material, the material being softer than the material of the spark plug sleeve. Between the gasket 18 and the Wall of the plug tube 19 in the cylinder head 20 is placed an adapter sleeve 21, preferably of harder metal, such as steel. The sleeve is tooled to lit tightly within the plug tube 19, and its outer surface conforms to the lower end of the tube plug, whatever the configuration may be. The inner wall of the adapter sleeve 21 is formed as a frusto-conical surface 22 which tapers inwardly toward the inner threaded end 15 of the spark plug, and which has a taper similar to that of the first frusto-conical surface on the spark plug. The threaded portion 15 of the plug is engaged with a threaded cornbustion chamber opening 23. Surrounding the plug tube are cooling water chambers 24 and 25 in the cylinder head 20, these water chambers having side walls 26, 27 and lower walls 28, 29, respectively.

Operation When the spark plug assembly is to be mounted in the cylinder head, the adapter sleeve 21 is first inserted into the plug tube 19, the surfaces being made clean and smooth. The copper gasket 18 is then fitted into the adapter sleeve, and the spark plug 10 is inserted and turned home in the threaded combustion chamber opening 23. As the spark plug 10 is tightened in said opening 23, the tapered surface 17 moves downwardly, expanding the copper gasket 18 and in turn expanding the adapter sleeve 21 and forcing it into tight engagement with the plug tube 19.

It will be noted that not only is the plug 10 tightly sealed relative to the combustion chamber opening 23, but, more important, an efficient, continuous, metallic heat liux path of relatively large cross-sectional area is established. Heat energy absorbed by the spark plug 10, as combustion occurs in the combustion chamber, passes through the truste-conical surface 17, through the copper gasket 18, through the adapter sleeve 21, and through the relatively thin side walls 26 and 27 of the cooling Water chambers 24 and 25 into the cooling water. A lesser and small amount of heat flux moves through the threaded portion 15, through the lower walls 28 and 29 of the cooling water chambers, and eventually outwardly into the cooling waters. The adapter sleeve 21 is preferably made longer than the frusto-conical surface 17, so that the cross-sectional area of the heat flux path is increased as the heat energy'moves from the spark plug 10 to the cooling water chambers 24 and 25.

While there has been herein shown and described the preferred embodiment of the invention, it is nevertheless to be understood that minor changes may be made therein without departing from the spirit and scope of the invention as claimed. For example, while the copper' gasket is to be preferred, it is conceivable that the invention might be accomplished by an adapter sleeve means of suitable material in direct engagement with vthe plug tube and having its inner frusto-conical surface in direct engagement with the frustro-conical surface formed on the sleeve of the spark plug.

What is claimed is:

1. In a spark plug assembly for water jacketed internal combustion engines having at least one plug tube extending through said water jacket, said plug tube being connected by a combustion chamber opening with a combustion chamber, and a spark plug having an inner end positioned within said opening, the combination therewith of means positioned axially outwardly from said inner end for providing a continuous, metallic heat flux path between said spark plug and said plug tube, said means including a rst frusto-conical surface on said spark plug tapering inwardly towards said inner end, an adapter sleeve tightly engaging said plug tube radially outwardly 0f said rst surface, and a second frustoconical surface on an inner wall of said adapter sleeve, said second surface tapering inwardly toward said inner end of said spark plug, the taper of first and second surfaces being similar.

2. A structure as set forth in claim 1, further including a frusto-conical metallic gasket between said rst and second surfaces.

3. A structure as set forth in claim l, wherein said adapter sleeve has an axial length greater than the axial length of the said rst frusto-conical surface.

4. A structure as set forth in claim 2, wherein said adapter sleeve has an axial length greater than the axial length of said frusto-conical gasket and said rst frustoconical surface on said spark plug.

5. A spark plug assembly for internal combustion engines comprising:

(a) a spark plug having an outer metallic sleeve,

(b) the sleeve being threaded at its inner end,

(c) a first frusto-conical surface on the sleeve positioned axially outwardly of the inner end,

(d) adapter sleeve means positioned radially outwardly of the rst frusto-conical surface,

(e) the adapter sleeve means having a second frustoconical surface adjacent to the rst frusto-conical surface and,

(f) a metallic gasket positioned between the first and the second frusto-conical surfaces, and in mating engagement with each of said surfaces.

6. A spark assembly as set forth in claim 5, wherein said adapter sleeve means has an axial length greater than the axial length of said first frusto-conical surface.

References Cited by the Examiner UNITED STATES PATENTS 2,113,629 4/38 Rabezzana 12S-41.32

2,212,725 8/40 Andres 123-169 2,870,760 1/59 Michaud S13- 11.5 X

FOREIGN PATENTS 1,020,489 12/ 57 Germany.

KARL I. ALBRECHT, Acting Primary Examiner. 

1. IN A SPARK PLUG ASEMBLY FOR WATER JACKETED INTERNAL COMBUSTION ENGINES HAVING AT LEAST ONE PLUG TUBE EXTENDING THROUGH SAID WATER JACKET, SAID PLUB TUBE BEING CONNECTED BY A COMBUSTION CHAMBER OPENING WITH A COMBUSTION CHAMBER, AND A SPARK PLUG HAVING AN INNER END POSITIONED WITHIN SAID OPENING, THE COMBNATION THEREWITH OF MEANS POSITIONED AXIALLY OUTWARDLY FROM SAID INNER END FOR PROVIDING A CONTINUOUS, METALLIC HEAT FLUX PATH BETWEEN SAID SPARK PLUG AND SAID PLUG TUBE, SAID MEANS INCLUDING A FIRST FRUSTO-CONICAL SURFACE ON SAID SPARK PLUG TAPERING INWARDLY TOWARDS SAID INNER END, AND ADAPTER SLEEVE TIGHTLY ENGAGING SAID PLUG TUBE RADIALLY OUTWARDLY OF SAID FIRST SURFACE, AND A SECOND FRUSTOCONICAL SURFACE ON AN INNER WALL OF SAID ADAPTER SLEEVE, 